Macimorelin

Identification

Name

Macimorelin

Accession Number

DB13074 (DB06066, DB05917)

Type

Small Molecule

Groups

Approved, Investigational

Description

Macimorelin, a novel and orally active ghrelin mimetic that stimulates GH secretion, is used in the diagnosis of adult GH deficiency (AGHD). More specifically, macimorelin is a peptidomimetic growth hormone secretagogue (GHS) that acts as an agonist of GH secretagogue receptor, or ghrelin receptor (GHS-R1a) to dose-dependently increase GH levels [3]. Growth hormone secretagogues (GHS) represent a new class of pharmacological agents which have the potential to be used in numerous clinical applications. They include treatment for growth retardation in children and cachexia associated with chronic disease such as AIDS and cancer.

Growth hormone (GH) is classically linked with linear growth during childhood. In deficiency of this hormone, AGHD is commonly associated with increased fat mass (particularly in the abdominal region), decreased lean body mass, osteopenia, dyslipidemia, insulin resistance, and/or glucose intolerance overtime. In addition, individuals with may be susceptible to cardiovascular complications from altered structures and function [5]. Risk factors of AGHD include a history of childhood-onset GH deficiency or with hypothalamic/pituitary disease, surgery, or irradiation to these areas, head trauma, or evidence of other pituitary hormone deficiencies [3]. While there are various therapies available such as GH replacement therapy, the absence of panhypopituitarism and low serum IGF-I levels with nonspecific clinical symptoms pose challenges to the detection and diagnosis of AGHD. The diagnosis of AGHD requires biochemical confirmation with at least 1 GH stimulation test [3]. Macimorelin is clinically useful since it displays good stability and oral bioavailability with comparable affinity to ghrelin receptor as its endogenous ligand. In clinical studies involving healthy subjects, macimorelin stimulated GH release in a dose-dependent manner with good tolerability [3].

Macimorelin, developed by Aeterna Zentaris, was approved by the FDA in December 2017 under the market name Macrilen for oral solution.

Pharmacology

Maximum GH levels from stimulation are observed between 30 to 90 minutes after administration of macimorelin [Label]. Increase in the QTcF interval may be observed from macimorelin administration [Label].

Mechanism of action

Ghrelin is an endogenous ligand for the GH secretagogue receptor that is also called the ghrelin receptor (GHS-R1a). Upon activation of the receptor, ghrelin serves to increase growth hormone (GH) secretion. Macimorelin mimics the actions of ghrelin by stimulating GH release. As a synthetic agonist, it activates growth hormone secretagogue receptors present in the pituitary and hypothalamus.

Macimorelin is a novel, synthetic ghrelin agonist, which is readily absorbed from the gastrointestinal tract [4]. The maximum plasma concentration (Cmax) was observed between 0.5 and 1.5 hours following oral administration of 0.5mg/kg macimorelin to patients with AGHD under fasting for at least 8 hours. Higher doses of drug demonstrate a dose-proportional increase in plasma concentrations [4]. A liquid meal decreased the macimorelin Cmax and AUC by 55% and 49%, respectively [Label].

Volume of distribution

Following a single oral dose of 0.5 mg/kg macimorelin, the mean volume of distribution of the central compartment is 5,733.4 ± 565.7L [4].

The mean terminal half-life (T1/2) is 4.1 hours following administration of a single oral dose of 0.5 mg macimorelin/kg body weight in healthy subjects [Label].

Clearance

Following a single oral dose of 0.5 mg/kg macimorelin, the mean clearance over the fraction absorbed (Cl/F) was 37,411.0 ± 4,554.6 mL/min [4].

Toxicity

Macimorelin has not shown to demonstrate mutagenic properties according to bacterial assays. It also did not induce any mutations or clastogenic effects in mouse lymphoma cells with or without metabolic activation. Studies assessing the carcinogenic potential or effect on fertility of macimorelin have not been conducted [Label].